1. Field of the Invention
This invention relates, in general, to photocopying and, more specifically, to controlling the development process and toner concentration in electrophotographic copiers and printers.
2. Description of the Prior Art
Electrostatographic apparatus, such a electrophotographic copiers and printers, which use a dry powdered toner to develop latent images usually require some type of monitoring and controlling device for maintaining consistency in the quality of the developed image. Toner concentration monitors are frequently used and a variety of systems have been seen and described in the prior art. The need for such systems is especially important when the size of the toner particle is reduced to allow for higher resolution in the developed image.
Conventional toner monitors includes types which measure the reflectance from a test or density patch developed with the toner mixture, measure reflectance directly from the toner in the hopper. and count the amount of pixels which are developed in the image when produced by an electronic exposure device. Other monitors use plates or electrodes located in or near the toner mixture to measure the steady state resistance, capacitance, or other parameter of the toner mixture. While these have all been proclaimed to provide some degree of success, other factors in the development process make the monitoring and control difficult to protect to a high degree of preciseness and better systems are always being studied.
The development rate is dependent upon not only the concentration of the toner but also upon other factors, such as the charge-to-mass ratio of the toner, the charge distribution, and the presence of wrong-sign particles. One prior art monitoring system which can provide information for toner and/or process control which achieves partial success in this regard uses an electrode or plate positioned above a magnetically actuated sample of the developer, or tone mixture. An electrostatic field is applied between the plate and the sample holder which causes toner to be developed or deposited on the plate. This provides and indication of the charge flow and weight of the developer. As with other systems, this system uses a steady state measurement of voltage or current in the monitor to indicate the toner conditions.
Many of the monitoring methods used or described in the prior art merely control the toner concentration or process control parameters based on the amount of toner in the mixture. Other factors, such as mass, time, humidity, and charge, ultimately affect the developed image. Therefore, it is desirable, and it is an object of this invention, to provide a toner development rate monitor and controller which gives improved development performance over prior art systems.